LTO and no_builtins: undefined references to standard Rust symbols errors at link time

[Deluvi]

It seems that depending on a Rust library that has the attribute #![no_builtins] prevents the linker to provide the needed symbols to the library.

I made a repository to demonstrate this issue with a minimal reproduction case: Deluvi/bug-no-builtins-lto-rust. The instructions to run the example are in the README.

Here is an example error line (you can find the whole cargo output in the "Error output" drop down below):

/usr/bin/ld: no_builtins_lib.2derfq4u-cgu.2:(.text._ZN5alloc7raw_vec19RawVec$LT$T$C$A$GT$7reserve17h791963cb9aa36cdbE+0x7f): undefined reference to `__rust_alloc'

If you want the compilation to work, you can remove the `#![no_builtins] line and the compilation will work just fine.

Meta

rustc --version --verbose:

rustc 1.43.1 (8d69840ab 2020-05-04)
binary: rustc
commit-hash: 8d69840ab92ea7f4d323420088dd8c9775f180cd
commit-date: 2020-05-04
host: x86_64-unknown-linux-gnu
release: 1.43.1
LLVM version: 9.0

Error output

cargo run --release -p no-builtins-bin
   Compiling no-builtins-lib v0.1.0 (/home/deluvi/tests/test-lto/no-builtins-lib)
   Compiling no-builtins-bin v0.1.0 (/home/deluvi/tests/test-lto/no-builtins-bin)
error: linking with `cc` failed: exit code: 1
  |
  = note: "cc" "-Wl,--as-needed" "-Wl,-z,noexecstack" "-m64" "-L" "/home/deluvi/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib" "/home/deluvi/tests/test-lto/target/release/deps/no_builtins_bin-d28e15586db11f8b.no_builtins_bin.ds5ffvdz-cgu.7.rcgu.o" "-o" "/home/deluvi/tests/test-lto/target/release/deps/no_builtins_bin-d28e15586db11f8b" "-Wl,--gc-sections" "-pie" "-Wl,-zrelro" "-Wl,-znow" "-Wl,-O1" "-nodefaultlibs" "-L" "/home/deluvi/tests/test-lto/target/release/deps" "-L" "/home/deluvi/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-Wl,-Bstatic" "/home/deluvi/tests/test-lto/target/release/deps/libno_builtins_lib-cef2adf5c7c12373.rlib" "-Wl,--start-group" "/tmp/rustcvFiUgJ/libbacktrace_sys-dc606003556dfe9c.rlib" "-Wl,--end-group" "/home/deluvi/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcompiler_builtins-2541f1e09df1c67d.rlib" "-Wl,-Bdynamic" "-ldl" "-lrt" "-lpthread" "-lgcc_s" "-lc" "-lm" "-lrt" "-lpthread" "-lutil" "-lutil"
  = note: /usr/bin/ld: /home/deluvi/tests/test-lto/target/release/deps/libno_builtins_lib-cef2adf5c7c12373.rlib(no_builtins_lib-cef2adf5c7c12373.no_builtins_lib.2derfq4u-cgu.0.rcgu.o): in function `core::ptr::drop_in_place':
          no_builtins_lib.2derfq4u-cgu.0:(.text._ZN4core3ptr13drop_in_place17h107dbe4e36e3489dE+0x13): undefined reference to `__rust_dealloc'
          /usr/bin/ld: /home/deluvi/tests/test-lto/target/release/deps/libno_builtins_lib-cef2adf5c7c12373.rlib(no_builtins_lib-cef2adf5c7c12373.no_builtins_lib.2derfq4u-cgu.2.rcgu.o): in function `alloc::raw_vec::RawVec<T,A>::reserve':
          no_builtins_lib.2derfq4u-cgu.2:(.text._ZN5alloc7raw_vec19RawVec$LT$T$C$A$GT$7reserve17h791963cb9aa36cdbE+0x58): undefined reference to `__rust_realloc'
          /usr/bin/ld: no_builtins_lib.2derfq4u-cgu.2:(.text._ZN5alloc7raw_vec19RawVec$LT$T$C$A$GT$7reserve17h791963cb9aa36cdbE+0x7f): undefined reference to `__rust_alloc'
          /usr/bin/ld: no_builtins_lib.2derfq4u-cgu.2:(.text._ZN5alloc7raw_vec19RawVec$LT$T$C$A$GT$7reserve17h791963cb9aa36cdbE+0x8f): undefined reference to `__rust_dealloc'
          /usr/bin/ld: no_builtins_lib.2derfq4u-cgu.2:(.text._ZN5alloc7raw_vec19RawVec$LT$T$C$A$GT$7reserve17h791963cb9aa36cdbE+0x98): undefined reference to `core::alloc::Layout::dangling'
          /usr/bin/ld: no_builtins_lib.2derfq4u-cgu.2:(.text._ZN5alloc7raw_vec19RawVec$LT$T$C$A$GT$7reserve17h791963cb9aa36cdbE+0xa8): undefined reference to `core::alloc::Layout::dangling'
          /usr/bin/ld: no_builtins_lib.2derfq4u-cgu.2:(.text._ZN5alloc7raw_vec19RawVec$LT$T$C$A$GT$7reserve17h791963cb9aa36cdbE+0xc4): undefined reference to `alloc::raw_vec::capacity_overflow'
          /usr/bin/ld: no_builtins_lib.2derfq4u-cgu.2:(.text._ZN5alloc7raw_vec19RawVec$LT$T$C$A$GT$7reserve17h791963cb9aa36cdbE+0xd4): undefined reference to `alloc::alloc::handle_alloc_error'
          collect2: error: ld returned 1 exit status
          

error: aborting due to previous error

error: could not compile `no-builtins-bin`.

[pnkfelix]

Inspired by discussion on PR #109821, I made a variant test case (largely taken from @dianqk's "stable" demo for that PR, to find out the historical behavior of Rust on that example. (The main differences are that 1. I changed the test to use extern crate, in order to be able to build on older versions of Rust, 2. I changed it to use lto = true rather than lto = fat, again for backward compatibility with older versions of Rust, and 3. I had the code start returning a non-() value from the linked crate, specially a &'static str, so that I could double-check that the dynamic behavior is plausible.)

Here is the main thing I've discovered so far: Rust 1.0 through 1.12 were able to compile and run the adapted example. It was back in Rust 1.13 that we started seeing this incompatbility between LTO and #![no_builtins], i.e. something along the lines of of:

% cargo  +1.13 build --release
   Compiling bar v0.1.0 (file:///home/ubuntu/Dev/Rust/Linking/issue_72140/rust-109821-reproducible/stable/bar)
   Compiling foo v0.1.0 (file:///home/ubuntu/Dev/Rust/Linking/issue_72140/rust-109821-reproducible/stable/foo)
   Compiling tool v0.1.0 (file:///home/ubuntu/Dev/Rust/Linking/issue_72140/rust-109821-reproducible/stable)
error: linking with `cc` failed: exit code: 1
  |
  = note: "cc" "-Wl,--as-needed" "-Wl,-z,noexecstack" "-m64" "-L" "/home/ubuntu/.rustup/toolchains/1.13-x86_64-unknown-linux-gnu/lib/rustlib/x86_6\
4-unknown-linux-gnu/lib" "/home/ubuntu/Dev/Rust/Linking/issue_72140/rust-109821-reproducible/stable/target/release/tool.0.o" "-o" "/home/ubuntu/De\
v/Rust/Linking/issue_72140/rust-109821-reproducible/stable/target/release/tool" "-Wl,--gc-sections" "-pie" "-nodefaultlibs" "-L" "/home/ubuntu/Dev\
/Rust/Linking/issue_72140/rust-109821-reproducible/stable/target/release/deps" "-L" "/home/ubuntu/.rustup/toolchains/1.13-x86_64-unknown-linux-gnu\
/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-Wl,-Bstatic" "-Wl,-Bdynamic" "/tmp/rustc.C74lmNfGlWwA/libfoo.rlib" "/tmp/rustc.C74lmNfGlWwA/libstd-a4\
729905.rlib" "/tmp/rustc.C74lmNfGlWwA/liballoc_jemalloc-a4729905.rlib" "/tmp/rustc.C74lmNfGlWwA/libcompiler_builtins-a4729905.rlib" "-l" "dl" "-l"\
 "pthread" "-l" "gcc_s" "-l" "pthread" "-l" "c" "-l" "m" "-l" "rt" "-l" "util"
  = note: /usr/bin/ld: /tmp/rustc.C74lmNfGlWwA/libfoo.rlib(foo.0.o): in function `foo::msg':
foo.cgu-0.rs:(.text._ZN3foo3msg17hb7b968140369922eE+0x1): undefined reference to `bar::msg'
collect2: error: ld returned 1 exit status

So, this has been broken for a long time (i.e. since the end of 2016), but it hasn't "always" been broken.

[dianqk]

Maybe now you could look at #113716. I added the no-builtins attribute to the function. We can get #![no_builtins] to participate in LTO again.

[pnkfelix]

Oh, was PR #35637 the reason that this broke between 1.12 and 1.13?

[dianqk]

Oh, was PR #35637 the reason that this broke between 1.12 and 1.13?

Yes. The symbols required by #![no_builtins] are present in LTO, but they are not exported. #109821 is a possible solution.
However, now I have found a more suitable solution, which is to let #![no_builtins] participate in LTO again.

[pnkfelix]

Yeah I think #113716 (plus reverting #35637) sounds far more reasonable than PR #109821.

(It still may not resolve some outstanding questions i have about what goes on with implicit dependencies on libcore, but that need not concern us here.)

[apiraino]

WG-prioritization assigning priority (Zulip discussion).

@rustbot label -I-prioritize +P-medium